Why Is the Komatsu SAA4D95LE-5 Engine Throwing Oil After Overhaul

[MikePhua]

The Komatsu PC130-8 and Its Engine Platform
The Komatsu PC130-8 is a mid-sized hydraulic excavator designed for utility work, road construction, and light earthmoving. It’s powered by the SAA4D95LE-5 engine, a four-cylinder turbocharged diesel unit developed by Komatsu to meet Tier 3 emissions standards. This engine is part of the 95 Series, known for its compact design, mechanical fuel injection, and relatively simple serviceability compared to later electronically controlled platforms.
Komatsu, founded in Japan in 1921, has long been a global leader in construction equipment. The PC130-8 was introduced in the mid-2000s and became popular in Asia, Latin America, and the Caribbean due to its balance of power, fuel efficiency, and ease of transport. While exact sales figures are proprietary, the PC130 series remains one of Komatsu’s most widely distributed excavators in the 13-ton class.
Post-Overhaul Oil Expulsion from the Breather
A troubling issue arises when the SAA4D95LE-5 engine begins throwing oil from the breather tube after a rebuild. This symptom typically appears under full load, such as during digging or hydraulic-intensive operations. The breather, which vents crankcase pressure, should only emit vapor or minimal mist. When oil is expelled in volume, it signals internal pressure imbalance or blow-by.
In one documented case, the engine had undergone a partial rebuild due to a piston pin failure that damaged cylinder #2. The repair included:

• One new cylinder sleeve
  
• New piston and connecting rod for #2
  
• Replacement crankshaft and bearings
  
• Genuine piston rings and seal kits
  

Despite these efforts, oil continued to exit the breather under load, even though the engine ran smoothly, showed no power loss, and emitted no smoke.
Root Causes of Breather Oil Blowout
Several factors can contribute to oil being forced out of the breather:

• Incorrect Ring Installation: If piston rings are installed upside down, especially the second compression ring (often a scraper ring), they fail to seal properly. This allows combustion gases to enter the crankcase, increasing pressure and forcing oil out.
  
• Cylinder Glazing: After initial ring seating, the cylinder walls develop a polished surface. Reinstalling used rings without honing the cylinder prevents proper sealing, leading to blow-by.
  
• Worn Valve Guides or Seals: While less common, excessive valve stem clearance can allow oil into the combustion chamber, increasing crankcase pressure indirectly.
  
• Turbocharger Seal Failure: A leaking turbo oil seal can pressurize the crankcase via the return line, though this usually presents with smoke or oil in the intake.
  
• Blocked Breather System: If the breather tube or separator is clogged, pressure builds up and oil is expelled forcefully.
  

In the case above, the rings were found installed upside down on all pistons. Although corrected, the cylinders were not re-honed, and the same rings were reused—likely contributing to continued blow-by.
Recommended Diagnostic and Repair Steps
To resolve breather oil expulsion:

• Perform a crankcase pressure test under load. Normal pressure should be below 2 psi; readings above 4 psi indicate excessive blow-by.
  
• Inspect breather tube and separator for blockage or oil saturation.
  
• Remove pistons and verify ring orientation. Replace rings if previously seated or damaged.
  
• Hone all cylinders lightly to break glaze and allow new rings to seat properly.
  
• Check turbo oil return line for restriction and inspect compressor housing for oil residue.
  
• Verify valve stem seals and guide clearance using a dial gauge or vacuum test.
  

Field Anecdotes and Lessons Learned
In Dominica, an operator rebuilt his PC130-8 engine after a piston pin failure. Despite replacing major components, oil continued to exit the breather. After discovering the ring orientation issue, he reinstalled them correctly but reused the same rings. The problem persisted, highlighting the importance of honing and using fresh components.
In Alberta, a contractor faced similar symptoms on a Komatsu WA100 loader. The cause was traced to a blocked breather separator filled with emulsified oil. Cleaning the separator and replacing the rings resolved the issue.
Preventive Measures and Long-Term Reliability
To ensure long-term engine health after overhaul:

• Always hone cylinders when installing new or reseated rings
  
• Use genuine or high-quality aftermarket rings with correct orientation markings
  
• Replace valve stem seals during top-end rebuilds
  
• Clean or replace breather assemblies every 1,000 hours
  
• Monitor crankcase pressure during routine service intervals
  
• Avoid partial rebuilds unless all tolerances are verified across cylinders
  

Conclusion
Oil expulsion from the breather in a Komatsu SAA4D95LE-5 engine is often a sign of internal pressure imbalance caused by ring misinstallation, poor seating, or overlooked wear. While the engine may run smoothly, the underlying issue can lead to long-term damage if not addressed. Proper rebuild practices—especially honing and ring replacement—are essential to restoring performance and preventing costly rework. In the world of diesel engines, precision matters more than appearance, and even a quiet-running machine can hide a brewing failure.